U.S. Pat. No. 3,823,585 describes a privacy lockset which may be locked only from the inside by pressing a push button and unlocked from the inside by rotating a knob or from the outside by turning a key. In the described lockset the driver spindle which drives the latch operating mechanism is always in driving engagement with the outside knob. Pressing of the push button causes a plunger to interlock the driver spindle with an inside clamp plate. The device includes many parts, making it expensive to manufacture.
Neary et al. U.S. Pat. No. 4,470,279 discloses a lockset which may be locked by pressing an inside push button. The push button drives a locking mechanism which links the outside knob to the inside chassis so that the outside knob will not turn. The lockset has no outside lock but a hole is provided in the outside knob for the insertion of a pick or special tool to unlock the lockset from the outside in case of an emergency. The pick moves a plunger bar axially and a tapered end of the plunger bar cams a locking element out of locking position thereby releasing the push button and unlocking the lockset.
Hale et al. U.S. Pat. No. 4,470,278 discloses a lockset wherein the locking function is accomplished by rotating a plunger bar, either by rotating a thumb-turn button located in the inside knob or rotating a lock plug in the outside knob with a key. Rotation of the plunger bar is translated into linear axial movement of a locking element which engages slots in an outside spindle and slots in an outside chassis to thereby lock the outside knob against rotation. Unlocking is accomplished by rotating the plunger bar by means of the thumb-turn button or by rotation of the lock plug in the outside knob.